Due to the characteristics of semiconductor, the output reference voltage of the reference voltage generation circuit has a temperature coefficient (abbreviated as TC) to compensate the temperature effect. For example, when an output reference voltage is 1.6V+10 mV/° C., the absolute voltage of the output reference voltage is 1.6V at specified temperature (ex: 25° C.), and the temperature coefficient is 10 mV/° C.
FIG. 1A shows output reference voltages having different absolute voltage values, wherein curves A1, B1 and C1 respectively indicate that the output reference voltage is 1.2V+10 mV/° C., 1.6V+10 mV/° C. and 2.0V+10 mV/° C. FIG. 1B shows output reference voltages having different temperature coefficients, wherein the curves A2, B2 and C2 respectively indicate that the output reference voltage is 1.6V+5 mV/° C., 1.6V+10 mV/° C. and 1.6V+15 mV/° C.
To adjust the absolute voltage value and the temperature coefficient, in a conventional reference voltage generation circuit, normally a bandgap circuit is used for generating a zero temperature coefficient voltage (zero-TC voltage) and a positive-TC voltage (positive-TC voltage), and an adder (or a subtractor) having buffers may be used for adding (or subtracting) the generated voltages to generate the output reference voltages with different temperature coefficients.
However, due to having the buffers, the conventional structure is too huge, and the power consumption and the circuit area are larger than other conventional circuits performing no temperature compensation. Besides, the buffers used in the addition/subtraction of voltages will incur extra offset, further severely affecting the accuracy in the output reference voltage and the temperature coefficient.